This invention relates to a pump-and-motor unit which is particularly adapted for supplying fuel and which comprises a pump rotor and motor armature the bearings of which are disposed independently of each other on a common fixed area.
The present invention relates to a fuel supply pump-and-motor unit of the type in which the pump rotor and motor armature are mounted on a common fixed axis provided by a longitudinally extending shaft element and include a rotation locking connection disposed between the rotor and motor armature.
In existing fuel supply units of this type the pump rotor and motor armature are mounted on a tubular element that telescopes the aforesaid shaft element. In another existing fuel supply unit, a connection bushing is disposed between the pump rotor and the motor armature; the inner bore of this connection bushing being arranged to receive a bearing which serves for both the pump rotor and the motor armature. However, it has been found that with this type of system there is excessive wear at the bearing points and also at the pump rotor, in spite of the fact that case-hardened sintered material has normally been used for the bearings. This excessive wear causes an increase in the current consumption; a reduction in the rpm, as well as the quantity of fuel supplied and ultimate pressure. This finally leads to complete failure of the fuel supply system for the internal combustion engine.
The excessive wear produced in existing pumps is due both to the poor lubricating properties of the new fuels and the relatively poor dry operating properties of the sintered bearings and also to the fact that the forces which the pump rotor and motor armature transmit to the bearings are markedly different. The pump rotor produces powerful radial forces directly on one end area of the longitudinally extending shaft whereas the motor armature produces powerful axial forces, particularly when starting up. These different stresses have been found to be especially hard on the rotating parts in the case of the rigid coupling systems of the existing fuel supply units, particularly when a common bearing is used. Marked radial stressing of the rotor produces radial wear of the associated bearings and, as a result, the motor armature can no longer operate concentrically which adversely affects the wear of the bearing disposed at the opposite end of the motor armature and also causes unilateral wear of the collector and irregular distribution of the magnetic forces. The axial forces of the motor armature on the pump rotor also cause a high degree of friction and corresponding wear between the rotor and the adjacent axial limiting wall of the pump.
Another disadvantage of the existing fuel supply units consists in that it is difficult to mount the corresponding parts, some of which fit in one another particularly since in some units the parts are pressed in succession into the cup-shaped unitized housing. As the housing acts as a support or guide for all elements contained therein tolerances in the radial dimensions are a disadvantage. This is particularly the case when a part of the fuel supply unit, such as the pump or motor, must be changed.